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Numerical simulation for pipe forming in multi-process hot extrusion


Numerical simulation for pipe forming in multi-process hot extrusion
Kun Chen , 80 Zhang ,Zhaotun Liu2 , Dingfang Chen 1 1 Intelligent Manu:facture and Control Institute of Wuhan University o.fTechnology chen_kl122@sina.com 2 Communication Planning and Design institute 0.1 Fujian liuzhaotun@126. com
1 1

Abstract
The numerical simulation method that pipe material forming in multi-process hot extnision was researched by FEM software ANSYS-LSDYNA. In the paper the cra;ft parameters, such as .friction , temperature, extrusion speed and the heat up length of the pipe, which affected the effect ofextrusion were analyzed and will provided theory re.ference when hot extrusion cra.ft were established.

Keywords:
simulatIon

pipe material, hot extrusion, numerical

1 Introduction
Metal plastic forming process simulation is the key technique which can design reasonable parameters of dies and draw better technical parameters at lower cost with short period, as well as describing the whole forming process. But achieving the numerical analysis successfully depends on various factors: including the shapes of the workpiece and tools, constructive relationship, the friction condition, temperature, velocity of the punch and length of calefaction for workpiece etc. It was a new technics that axes accessory was got by the shrinking of steel tube, with the process of hot extrusion of the whole workpiece, the productivity could be improved evidently and the cost could be down. The benefit of economy is imnlensity, such as the behind bridge of automobile is a typical axes pipe accessory.

conlplicated, so the contacting state are changed constantly, friction also can hardly be described, at the same time, there are coupling of hot and force between workpiece and dies, and there are many effected technology parameters. Also of this, it can hardly be gained accuracy solutions in the extrusion forming. Now finite element method is the most effective tool to solve nonlinear questions and simulate the metal flow process, which can solve arbitrary boundaries and multi materials at the base of sufficient precision. In the text, Finite element analyzing software Ansys and Ls-Oyna were used for modeling and analyzing. Considering the pipe in the text as an axis symmetry part, the 20 axis symmetry model was used to save simulation storage room and itnprove calculation efficiency.

2.2 Material Characteristic
The material 20Cr was used as the workpiece material, and hot die steel 35CrMnSi(H13) was used as the die material. In the FEA sinlulation, the dies were assumed as rigid body, which have no distortion, only have heat transferring with workpiece. The workpiece was distorted at the force of top die. Because the field strength changed as temperature changed, there will be greatly infection to the distortion, we should consider the flow stress and strain curve (shown in Figure 1) in different temperature.

~

'100

2 FEA Simulation
2.1 The FEA model
Hot extrusion is a very complicated process, for the workpiece distorted greatly, there are geometrical nonlinear in the relation of displacement and strain and material nonlinear in the material constructive relationship (that is physical nonlinear). On the other hand, the dies geometrical shapes are often very
978-1-4244-3291-2/08/$25.00 ?2008 IEEE

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~

~600

;500

l.

Figure1 The workpiece characteristic curve in different temperature

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Figure2 Temperature contour of the pipe after heating in the furnace

2.3 The processe simulation and discussion
2.3.1 Preparation. The length of the workpiece was 675mm, and the heating length was 400mm, the workpiece was heated in the intermediate frequency induction furnace of 1000°C for 40 minutes. 2D axis symmetry element Plane55 was used to model; the workpiece temperature contour at Figure2 was gain after FEA calculation. The highest temperature in the workpiece was 1000 °c, the lowest temperature in the top part which was not heated, the lowest temperature was 30 °c.
Fringe Levels

2.3.2 First step extrusion. The 2D axis symmetry thermal element Plane55 in the heating step was changed to Explicit Dynamics 2D axis symmetry element Plane 162, at the same time, the Models of top die, bottom die and Ejector Pin were built in Pre-processor of Ansys/Ls-Dyna. And then they were appointed material, real constant and element type properties and meshed. After that, K file which Ls-Dyna solver only can identify was exported. The points sets of top die, bottom die and ejector pin were added in K file, then initial uniform temperature were applied to these points sets separately, that is: the workpiece with uneven temperature distribution from 30 °c to 1000 °c, bottom die 250 °c, top die and ejector pin 20 °C. The initial model of first extrusion step were got(shown in Figure 3).
The extrusion process can finished successfully at the condition that the parameters are reasonable. The extrusion process was shown in Figure 4.

2.3.3The second step hot extrusion. The first step
result data can't be saved for the second hot extrusion step in Ls-Dyna, So the element birth and death method was used for the first step to second step to realize the two steps formation of the pipe. The extrusion process was shown in Figure 5.
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Figure3 The assembly model and temperature distribution of first hot extrusion step
FrtngeLevels
7.7~e+08

Figures Extrusion process of second step and stress contour

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4.&1Oe~
3.l108e~ 3.046e~

2.3.4 Infection of technological parameters. The infection of various technical parameters to forming effects can be gained conveniently by the simulation test. The simulation result showed that proper technological parameters can impel the extrusion process finished successfully, and vice versa, even worse, the extrusion process can't finish successfully. As the Figure 6 show, it is a comparison of forming shapes at different friction coefficients.

(a) (b) Figure4 The first step hot extrusion and stress contour

686

1.204 x 10-4

0

3 Conclusions
The Numerical simulation of pipe extrusion effects with multi steps were researched by examples. The distributions of distortion, temperature, stress and strain were gained by numerical simulation, At the same time, the failing extrusion was simulated too which can help us to making proper parameters for different extrusion condition. The extrusion process can be finished by adjusting workpiece temperature, friction and extrusion velocity properly, but the shapes of dies weren't transformed greatly. In a word, numerical simulation can improve the design period greatly, and decrease the production cost. It is an effective method to forecast the forming effect and optimize the technological parameters.

f=0 f=0.1 [=0.2 f=0.3 Figure6 Metal accumulation phenomenon at different friction coefficients The infection of friction coefficient, extrusion velocity and heating temperature to forming effect was considered integrated, and Numerical Analysis was used, the predictive Formula about pipe forming effect was gained. The experiment result show that there is a good effect for the formula to the selection of technological parameters

Acknowledgement
National 863 Plan, The develop and application of ASP service platform faced on Automobile and equipment industrial chin (2003AA414011) Fifteen significant technology tackling project of Wuhan: Research and Application of distributed virtual design and virtual manufacture (2001001003 )

y=a o +a,x. +a 2 x 2 +a 3 x 3 +b,x~ +
b2X~ +b3 x; +c.x.x2 +C 2X.X 3 +C 3 X2X3
Where: Dependent variable: y is Closeness Degree (%) Independent variable:
XI is friction coefficient;

(1)

References
[1] Zhao liachang, Wang Zhongren, Experiment verification of extrusion force of hot extrusion aluminum alloy bar. Heavy Machinery. 1982,10,31-38 [2] Zhou Yimiao. Extrusion Force Calculation of Metal Profile. Heavy Machinery. 1991,4,31-40 [3] Yu Hanqing, Chen linde. The Theory of Metal Plastic Forming. China Machine Press. 1999, 10(1),30-200 [4] Kun Chen,Bo Zhang, DingFang Chen.The Research and Optimization of the Complex Extrusion Technology of Half-axel with Flang. Journal of Computeational Information Systems,Volume 3,Number 2,2007

x 2 is extrusion velocity(mln/s); x 3 is the workpiece heating temperature( °C).
Coefficient:

ao ==77.81; al == 18.99;

a2

==0.1161;
4 ;

a3 ==0.0371 ;

hi

==285.92;

b2 == 1.045 x 10-

b3 == 1.517x 10-5 ;

ci ==0.9135;

c2 ==1.746xl0-2

;

c3 ==

tlR7


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